In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization of a pattern. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation such as g-line and i-line radiation has been used, but nowadays, mass production of semiconductor elements using KrF excimer lasers and ArF excimer lasers has commenced, and technology that uses extreme ultraviolet (EUV) or an electron beam (EB) as the radiation source is also attracting considerable attention. Furthermore, one example of a known pattern-forming material capable of forming a pattern of minute dimensions is a chemically amplified resist, which includes a base material component with a film-forming capability, and an acid generator component that generates an acid upon exposure. Chemically amplified resists include negative compositions, which undergo a reduction in alkali solubility on exposure, and positive compositions, which exhibit increased alkali solubility on exposure. Conventionally, polymers are used as the base material component.
When a pattern is formed using this type of pattern-forming material, a problem arises in that roughness is generated on the upper surface and side wall surfaces of the pattern, and this problem becomes more severe as the pattern dimensions are reduced. For example, because EUV and EB lithography are targeting the formation of very fine patterns of several tens of nm, ultra low levels of roughness surpassing the current levels of pattern roughness are required.
However, the polymers that are typically used as base materials have a large molecular size (root mean squared radius per molecule) of approximately several nm. During the developing step of the pattern formation process, the dissolution behavior of the resist in the developing solution usually occurs at the single molecular unit level of the base material, meaning that as long as a polymer is used as the base material component, further reductions in the level of roughness will prove extremely difficult.
In response to these problems, resists that use low molecular weight materials as the base material component have been proposed as materials capable of targeting ultra low levels of roughness. For example, patent references 1 and 2 propose low molecular weight materials containing alkali-soluble groups such as hydroxyl groups, wherein either a portion of, or all of, the alkali-soluble groups are protected with acid-dissociable, dissolution-inhibiting groups. These low molecular weight materials have small molecular sizes as a result of their lower molecular weight, and are expected to enable reductions in the level of roughness.
(Patent Reference 1)
Japanese Unexamined Patent Application, First Publication No. 2002-099088
(Patent Reference 2)
Japanese Unexamined Patent Application, First Publication No. 2002-099089